Impulse and step voltage measurements on materials with non-linear V-I characteristic

Nonlinear Field Grading Materials (FGM) are used in high voltage engineering for electric field control. The material parameters of interest include low field conductivity, threshold voltage and the nonlinearity coefficient. The difficulty in measuring the dielectric properties arises from the ohmic heating in the material at high field. Several methods have been proposed to measure the dielectric properties of FGMs at high field, impulse measurements and single period dielectric spectroscopy being the most prominent. Another possibility is to measure the conductivity with step voltages applied for a limited time to be able to achieve a high field with no or little heating in the material. Impulse measurements and step voltage measurements have been performed on field grading materials and an example of the corresponding analysis and results are shown as well as an overview of the measurement systems used. A comparison of the different techniques is also presented.